The present invention relates to a tubular type ozone generator and an inner electrode thereof.
Ozone generators of the tubular type, and which operate under the principle of silent discharge, are known and include an outer electrically conductive tubular electrode, a dielectric tube positioned within the outer tubular electrode and spaced therefrom to form a discharge gap, and an inner electrode contacting the inner surface of the dielectric tube. Conventionally, the inner electrode is in the form of a metal layer coated over the inner surface of the dielectric tube. The outer electrode and the inner electrode are connected to opposite terminals of a high voltage AC source, such that when a voltage is applied between the inner and outer electrodes and across the discharge gap, then an oxygen containing gas circulated through the discharge gap is transformed into ozone by means of a well understood phenomenon generally referred to as "silent discharge."
Ozone generator systems normally include a plurality of parallely arranged generators of the above type.
The dielectric tube normally is a glass cylinder having a constant thickness and having one end closed in the form of a spherical, conical or even flat bottom, with the other end being open. The dielectric tube is positioned concentrically within an outer tubular member, normally a metal cylinder, which forms the outer electrode. An annular, constant thickness gap between the dielectric tube and the outer tubular electrode forms a discharge gap through which is circulated an oxygen containing gas, for example oxygen or air.
This type of arrangement forms a capacitor including an outer electrode formed by the metal tubular member, an inner electrode formed by the metal coating, and a pair of dielectrics, the first being solid and formed by the glass tube and the second being gaseous and formed by the discharge gap.
Generally, the glass tube and the metal coating on the inner surface thereof are conventionally referred to as a "high voltage electrode," while the outer metal tubular electrode is conventionally referred to as a "low voltage electrode" or a "ground electrode".
As is further conventional in the art, the high voltage electrode is connected to a terminal of a high voltage AC source by means of a brush shaped metal connector which is inserted into the glass tube and which electrically contacts the metal layer on the inner surface thereof. The high voltage AC source may be any locally available supply circuit having the necessary intermediate or high frequencies, for example approximately between 50 and 5,000 cycles per second. The low voltage terminal of the source is grounded, and conventionally the low voltage or outer electrode of the ozone generator is grounded, for example by connection to the low voltage terminal of the source.
When a voltage is applied between the two electrodes of the ozone generator, and when a flow of air or oxygen is continuously circulated through the discharge gap, and when the applied voltage reaches a certain value, a phenomenon known as "silent discharge" occurs across the discharge gap, thereby transforming a portion of the oxygen in the discharge gap into ozone.
For a constant flow of gas, a constant gas pressure and for a discharge gap of a given size, the amount of ozone produced by this type of apparatus will increase as a function of increased voltage applied between the inner and outer electrodes. However, in employing conventional prior art ozone generators of this type, the maximum value of such applied voltage is limited to a value substantially less than that which would theoretically be possible. Specifically, when the applied potential reaches a certain value less than the theoretical maximum value, a parasitic discharge or sparking occurs between the outer electrode and the end of the inner electrode adjacent the open end of the glass tube. More particularly, the lines of force of the electric field which is generated concentrate at the outer end of the inner electrode, and this concentration of lines of force results in the emission of sparks.
Such sparks result in a reduction in the efficiency of the ozone generator, since the sparks do not contribute to the generation of ozone, and since this concentration of the lines of force may result in local deterioration of the material of the generator and can result in a short circuit. Thus, conventional ozone generators of this type cannot be operated above a certain potential difference, for example 20,000 volts.
One prior art attempt to eliminate such sparking is disclosed in French Pat. No, 1,530,551 and discloses a metal ring having a cylindrical portion in contact with the metal coating forming the inner electrode and an inwardly curved portion having a parabolic configuration and extending outwardly beyond the outer end of the inner electrode. The brush shaped contact is joined to a terminal of the high voltage AC source by means of a connector which extends through the open end of the curved portion of the metal ring. In this type of arrangement, since the metal ring is curved away from the outer electrode, the effect of sparking between the outer electrode and the outer end of the inner electrode is reduced.
However, even the arrangement of French Pat. No. 1,530,551 is not entirely satisfactory.